Relaxation of the leaf economics spectrum within and across quaking aspen <i>Populus tremuloides</i> genotypes

Plant functional traits typically show strong covariation, e.g. as in the worldwide leaf economics spectrum (LES). Covariation is thought to arise from selective forces and physical constraints. However, processes shaping covariation at interspecific scales may differ from those at intraspecific scales. Potential sources of intraspecific trait variation include variation in genetics, abiotic environment, and biotic environment; any of these factors may cause divergence from interspecific patterns. Quaking aspen, Populus tremuloides (Salicaceae), is a widespread tree species ideal for assessing these processes' role in the intraspecific LES, due to its clonal growth along environmental gradients, intraspecific variation in cytotype (ploidy level), and variation in biotic interactions (herbivory pressure). Here, we investigate genotype, cytotype, microclimate and herbivory as potential drivers in shaping LES trait–trait and trait–environment relationships at intra‐specific scales. We studied 15 quaking aspen genotypes that varied in cytotype (diploid or triploid) along an elevation gradient in southwestern Colorado. We show that LES tradeoffs substantially weaken at the intraspecific scale in this species. Among genotypes, trait–trait slopes ranged from positive, weak, strong, negative, or absent compared to the global LES. We also found that cytotypes varied in resource‐use tradeoffs, and that increasing insect herbivory pressure decreased the strength of several trait–trait relationships. Microenvironment was a weak predictor of intraspecific functional trait variation in quaking aspen. Synthesis. In quaking aspen, there are relaxed constraints on LES trait co‐variation. Variation in genotype, cytotype, and herbivory pressure each contribute to this pattern. Relaxation of the LES may enable more flexible responses to environmental stressors through both genetic and plastic mechanisms.